The fabrication of semiconductor nanostructures is becoming increasingly important for both research and industrial applications. Emerging technologies and devices, such as photonic crystals, functional metamaterials and through-silicon vias (TSVs), require high resolution and high aspect ratio nanofabrication techniques for enhanced performance. Unfortunately, current nanofabrication techniques, such as plasma etching, deep reactive ion etching and ion etching, suffer from various shortcomings, including the formation of features with rough scalloped side walls and/or surface damage and defects that degrade the device performance significantly.
Metal-assisted chemical etching (MacEtch) is a wet but directional etching technique for etching features in semiconductors. In a typical MacEtch process, a patterned metal film is applied to a semiconductor surface to act as a catalyst to guide etching of the underlying semiconductor when exposed to a suitable etchant, which typically includes an oxidant, such as H2O2 or KMnO4, and an acid, such as HF. During etching, the metal film sinks into the underlying semiconductor, effectively carving out 3D semiconductor structures according to the 2D pattern of the metal film. The role of the catalyst may including reducing the oxidant and selectively enhancing the oxidation rate of the underlying semiconductor by hole carrier injection. The role of the acid may include dissolving the oxidized semiconductor to allow continued oxidation and etching in a direction normal to the semiconductor-metal interface. A challenge with MacEtch, when the patterned metal film takes the form of discrete metal features such as metal particles or metal disks, is that uncontrolled lateral motion or delamination of the discrete metal features may occur during etching, leading to structural defects and/or non-vertical features in the etched semiconductor.